File size: 41,933 Bytes
b334e29
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
# Copyright (c) OpenMMLab. All rights reserved.
import inspect
import os
import os.path as osp
import re
import tempfile
import warnings
from abc import ABCMeta, abstractmethod
from contextlib import contextmanager
from pathlib import Path
from typing import Iterable, Iterator, Optional, Tuple, Union
from urllib.request import urlopen

import annotator.uniformer.mmcv as mmcv
from annotator.uniformer.mmcv.utils.misc import has_method
from annotator.uniformer.mmcv.utils.path import is_filepath


class BaseStorageBackend(metaclass=ABCMeta):
    """Abstract class of storage backends.

    All backends need to implement two apis: ``get()`` and ``get_text()``.
    ``get()`` reads the file as a byte stream and ``get_text()`` reads the file
    as texts.
    """

    # a flag to indicate whether the backend can create a symlink for a file
    _allow_symlink = False

    @property
    def name(self):
        return self.__class__.__name__

    @property
    def allow_symlink(self):
        return self._allow_symlink

    @abstractmethod
    def get(self, filepath):
        pass

    @abstractmethod
    def get_text(self, filepath):
        pass


class CephBackend(BaseStorageBackend):
    """Ceph storage backend (for internal use).

    Args:
        path_mapping (dict|None): path mapping dict from local path to Petrel
            path. When ``path_mapping={'src': 'dst'}``, ``src`` in ``filepath``
            will be replaced by ``dst``. Default: None.

    .. warning::
        :class:`mmcv.fileio.file_client.CephBackend` will be deprecated,
        please use :class:`mmcv.fileio.file_client.PetrelBackend` instead.
    """

    def __init__(self, path_mapping=None):
        try:
            import ceph
        except ImportError:
            raise ImportError('Please install ceph to enable CephBackend.')

        warnings.warn(
            'CephBackend will be deprecated, please use PetrelBackend instead')
        self._client = ceph.S3Client()
        assert isinstance(path_mapping, dict) or path_mapping is None
        self.path_mapping = path_mapping

    def get(self, filepath):
        filepath = str(filepath)
        if self.path_mapping is not None:
            for k, v in self.path_mapping.items():
                filepath = filepath.replace(k, v)
        value = self._client.Get(filepath)
        value_buf = memoryview(value)
        return value_buf

    def get_text(self, filepath, encoding=None):
        raise NotImplementedError


class PetrelBackend(BaseStorageBackend):
    """Petrel storage backend (for internal use).

    PetrelBackend supports reading and writing data to multiple clusters.
    If the file path contains the cluster name, PetrelBackend will read data
    from specified cluster or write data to it. Otherwise, PetrelBackend will
    access the default cluster.

    Args:
        path_mapping (dict, optional): Path mapping dict from local path to
            Petrel path. When ``path_mapping={'src': 'dst'}``, ``src`` in
            ``filepath`` will be replaced by ``dst``. Default: None.
        enable_mc (bool, optional): Whether to enable memcached support.
            Default: True.

    Examples:
        >>> filepath1 = 's3://path/of/file'
        >>> filepath2 = 'cluster-name:s3://path/of/file'
        >>> client = PetrelBackend()
        >>> client.get(filepath1)  # get data from default cluster
        >>> client.get(filepath2)  # get data from 'cluster-name' cluster
    """

    def __init__(self,
                 path_mapping: Optional[dict] = None,
                 enable_mc: bool = True):
        try:
            from petrel_client import client
        except ImportError:
            raise ImportError('Please install petrel_client to enable '
                              'PetrelBackend.')

        self._client = client.Client(enable_mc=enable_mc)
        assert isinstance(path_mapping, dict) or path_mapping is None
        self.path_mapping = path_mapping

    def _map_path(self, filepath: Union[str, Path]) -> str:
        """Map ``filepath`` to a string path whose prefix will be replaced by
        :attr:`self.path_mapping`.

        Args:
            filepath (str): Path to be mapped.
        """
        filepath = str(filepath)
        if self.path_mapping is not None:
            for k, v in self.path_mapping.items():
                filepath = filepath.replace(k, v)
        return filepath

    def _format_path(self, filepath: str) -> str:
        """Convert a ``filepath`` to standard format of petrel oss.

        If the ``filepath`` is concatenated by ``os.path.join``, in a Windows
        environment, the ``filepath`` will be the format of
        's3://bucket_name\\image.jpg'. By invoking :meth:`_format_path`, the
        above ``filepath`` will be converted to 's3://bucket_name/image.jpg'.

        Args:
            filepath (str): Path to be formatted.
        """
        return re.sub(r'\\+', '/', filepath)

    def get(self, filepath: Union[str, Path]) -> memoryview:
        """Read data from a given ``filepath`` with 'rb' mode.

        Args:
            filepath (str or Path): Path to read data.

        Returns:
            memoryview: A memory view of expected bytes object to avoid
                copying. The memoryview object can be converted to bytes by
                ``value_buf.tobytes()``.
        """
        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        value = self._client.Get(filepath)
        value_buf = memoryview(value)
        return value_buf

    def get_text(self,
                 filepath: Union[str, Path],
                 encoding: str = 'utf-8') -> str:
        """Read data from a given ``filepath`` with 'r' mode.

        Args:
            filepath (str or Path): Path to read data.
            encoding (str): The encoding format used to open the ``filepath``.
                Default: 'utf-8'.

        Returns:
            str: Expected text reading from ``filepath``.
        """
        return str(self.get(filepath), encoding=encoding)

    def put(self, obj: bytes, filepath: Union[str, Path]) -> None:
        """Save data to a given ``filepath``.

        Args:
            obj (bytes): Data to be saved.
            filepath (str or Path): Path to write data.
        """
        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        self._client.put(filepath, obj)

    def put_text(self,
                 obj: str,
                 filepath: Union[str, Path],
                 encoding: str = 'utf-8') -> None:
        """Save data to a given ``filepath``.

        Args:
            obj (str): Data to be written.
            filepath (str or Path): Path to write data.
            encoding (str): The encoding format used to encode the ``obj``.
                Default: 'utf-8'.
        """
        self.put(bytes(obj, encoding=encoding), filepath)

    def remove(self, filepath: Union[str, Path]) -> None:
        """Remove a file.

        Args:
            filepath (str or Path): Path to be removed.
        """
        if not has_method(self._client, 'delete'):
            raise NotImplementedError(
                ('Current version of Petrel Python SDK has not supported '
                 'the `delete` method, please use a higher version or dev'
                 ' branch instead.'))

        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        self._client.delete(filepath)

    def exists(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path exists.

        Args:
            filepath (str or Path): Path to be checked whether exists.

        Returns:
            bool: Return ``True`` if ``filepath`` exists, ``False`` otherwise.
        """
        if not (has_method(self._client, 'contains')
                and has_method(self._client, 'isdir')):
            raise NotImplementedError(
                ('Current version of Petrel Python SDK has not supported '
                 'the `contains` and `isdir` methods, please use a higher'
                 'version or dev branch instead.'))

        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        return self._client.contains(filepath) or self._client.isdir(filepath)

    def isdir(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a directory.

        Args:
            filepath (str or Path): Path to be checked whether it is a
                directory.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a directory,
                ``False`` otherwise.
        """
        if not has_method(self._client, 'isdir'):
            raise NotImplementedError(
                ('Current version of Petrel Python SDK has not supported '
                 'the `isdir` method, please use a higher version or dev'
                 ' branch instead.'))

        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        return self._client.isdir(filepath)

    def isfile(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a file.

        Args:
            filepath (str or Path): Path to be checked whether it is a file.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a file, ``False``
                otherwise.
        """
        if not has_method(self._client, 'contains'):
            raise NotImplementedError(
                ('Current version of Petrel Python SDK has not supported '
                 'the `contains` method, please use a higher version or '
                 'dev branch instead.'))

        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        return self._client.contains(filepath)

    def join_path(self, filepath: Union[str, Path],
                  *filepaths: Union[str, Path]) -> str:
        """Concatenate all file paths.

        Args:
            filepath (str or Path): Path to be concatenated.

        Returns:
            str: The result after concatenation.
        """
        filepath = self._format_path(self._map_path(filepath))
        if filepath.endswith('/'):
            filepath = filepath[:-1]
        formatted_paths = [filepath]
        for path in filepaths:
            formatted_paths.append(self._format_path(self._map_path(path)))
        return '/'.join(formatted_paths)

    @contextmanager
    def get_local_path(self, filepath: Union[str, Path]) -> Iterable[str]:
        """Download a file from ``filepath`` and return a temporary path.

        ``get_local_path`` is decorated by :meth:`contxtlib.contextmanager`. It
        can be called with ``with`` statement, and when exists from the
        ``with`` statement, the temporary path will be released.

        Args:
            filepath (str | Path): Download a file from ``filepath``.

        Examples:
            >>> client = PetrelBackend()
            >>> # After existing from the ``with`` clause,
            >>> # the path will be removed
            >>> with client.get_local_path('s3://path/of/your/file') as path:
            ...     # do something here

        Yields:
            Iterable[str]: Only yield one temporary path.
        """
        filepath = self._map_path(filepath)
        filepath = self._format_path(filepath)
        assert self.isfile(filepath)
        try:
            f = tempfile.NamedTemporaryFile(delete=False)
            f.write(self.get(filepath))
            f.close()
            yield f.name
        finally:
            os.remove(f.name)

    def list_dir_or_file(self,
                         dir_path: Union[str, Path],
                         list_dir: bool = True,
                         list_file: bool = True,
                         suffix: Optional[Union[str, Tuple[str]]] = None,
                         recursive: bool = False) -> Iterator[str]:
        """Scan a directory to find the interested directories or files in
        arbitrary order.

        Note:
            Petrel has no concept of directories but it simulates the directory
            hierarchy in the filesystem through public prefixes. In addition,
            if the returned path ends with '/', it means the path is a public
            prefix which is a logical directory.

        Note:
            :meth:`list_dir_or_file` returns the path relative to ``dir_path``.
            In addition, the returned path of directory will not contains the
            suffix '/' which is consistent with other backends.

        Args:
            dir_path (str | Path): Path of the directory.
            list_dir (bool): List the directories. Default: True.
            list_file (bool): List the path of files. Default: True.
            suffix (str or tuple[str], optional):  File suffix
                that we are interested in. Default: None.
            recursive (bool): If set to True, recursively scan the
                directory. Default: False.

        Yields:
            Iterable[str]: A relative path to ``dir_path``.
        """
        if not has_method(self._client, 'list'):
            raise NotImplementedError(
                ('Current version of Petrel Python SDK has not supported '
                 'the `list` method, please use a higher version or dev'
                 ' branch instead.'))

        dir_path = self._map_path(dir_path)
        dir_path = self._format_path(dir_path)
        if list_dir and suffix is not None:
            raise TypeError(
                '`list_dir` should be False when `suffix` is not None')

        if (suffix is not None) and not isinstance(suffix, (str, tuple)):
            raise TypeError('`suffix` must be a string or tuple of strings')

        # Petrel's simulated directory hierarchy assumes that directory paths
        # should end with `/`
        if not dir_path.endswith('/'):
            dir_path += '/'

        root = dir_path

        def _list_dir_or_file(dir_path, list_dir, list_file, suffix,
                              recursive):
            for path in self._client.list(dir_path):
                # the `self.isdir` is not used here to determine whether path
                # is a directory, because `self.isdir` relies on
                # `self._client.list`
                if path.endswith('/'):  # a directory path
                    next_dir_path = self.join_path(dir_path, path)
                    if list_dir:
                        # get the relative path and exclude the last
                        # character '/'
                        rel_dir = next_dir_path[len(root):-1]
                        yield rel_dir
                    if recursive:
                        yield from _list_dir_or_file(next_dir_path, list_dir,
                                                     list_file, suffix,
                                                     recursive)
                else:  # a file path
                    absolute_path = self.join_path(dir_path, path)
                    rel_path = absolute_path[len(root):]
                    if (suffix is None
                            or rel_path.endswith(suffix)) and list_file:
                        yield rel_path

        return _list_dir_or_file(dir_path, list_dir, list_file, suffix,
                                 recursive)


class MemcachedBackend(BaseStorageBackend):
    """Memcached storage backend.

    Attributes:
        server_list_cfg (str): Config file for memcached server list.
        client_cfg (str): Config file for memcached client.
        sys_path (str | None): Additional path to be appended to `sys.path`.
            Default: None.
    """

    def __init__(self, server_list_cfg, client_cfg, sys_path=None):
        if sys_path is not None:
            import sys
            sys.path.append(sys_path)
        try:
            import mc
        except ImportError:
            raise ImportError(
                'Please install memcached to enable MemcachedBackend.')

        self.server_list_cfg = server_list_cfg
        self.client_cfg = client_cfg
        self._client = mc.MemcachedClient.GetInstance(self.server_list_cfg,
                                                      self.client_cfg)
        # mc.pyvector servers as a point which points to a memory cache
        self._mc_buffer = mc.pyvector()

    def get(self, filepath):
        filepath = str(filepath)
        import mc
        self._client.Get(filepath, self._mc_buffer)
        value_buf = mc.ConvertBuffer(self._mc_buffer)
        return value_buf

    def get_text(self, filepath, encoding=None):
        raise NotImplementedError


class LmdbBackend(BaseStorageBackend):
    """Lmdb storage backend.

    Args:
        db_path (str): Lmdb database path.
        readonly (bool, optional): Lmdb environment parameter. If True,
            disallow any write operations. Default: True.
        lock (bool, optional): Lmdb environment parameter. If False, when
            concurrent access occurs, do not lock the database. Default: False.
        readahead (bool, optional): Lmdb environment parameter. If False,
            disable the OS filesystem readahead mechanism, which may improve
            random read performance when a database is larger than RAM.
            Default: False.

    Attributes:
        db_path (str): Lmdb database path.
    """

    def __init__(self,
                 db_path,
                 readonly=True,
                 lock=False,
                 readahead=False,
                 **kwargs):
        try:
            import lmdb
        except ImportError:
            raise ImportError('Please install lmdb to enable LmdbBackend.')

        self.db_path = str(db_path)
        self._client = lmdb.open(
            self.db_path,
            readonly=readonly,
            lock=lock,
            readahead=readahead,
            **kwargs)

    def get(self, filepath):
        """Get values according to the filepath.

        Args:
            filepath (str | obj:`Path`): Here, filepath is the lmdb key.
        """
        filepath = str(filepath)
        with self._client.begin(write=False) as txn:
            value_buf = txn.get(filepath.encode('ascii'))
        return value_buf

    def get_text(self, filepath, encoding=None):
        raise NotImplementedError


class HardDiskBackend(BaseStorageBackend):
    """Raw hard disks storage backend."""

    _allow_symlink = True

    def get(self, filepath: Union[str, Path]) -> bytes:
        """Read data from a given ``filepath`` with 'rb' mode.

        Args:
            filepath (str or Path): Path to read data.

        Returns:
            bytes: Expected bytes object.
        """
        with open(filepath, 'rb') as f:
            value_buf = f.read()
        return value_buf

    def get_text(self,
                 filepath: Union[str, Path],
                 encoding: str = 'utf-8') -> str:
        """Read data from a given ``filepath`` with 'r' mode.

        Args:
            filepath (str or Path): Path to read data.
            encoding (str): The encoding format used to open the ``filepath``.
                Default: 'utf-8'.

        Returns:
            str: Expected text reading from ``filepath``.
        """
        with open(filepath, 'r', encoding=encoding) as f:
            value_buf = f.read()
        return value_buf

    def put(self, obj: bytes, filepath: Union[str, Path]) -> None:
        """Write data to a given ``filepath`` with 'wb' mode.

        Note:
            ``put`` will create a directory if the directory of ``filepath``
            does not exist.

        Args:
            obj (bytes): Data to be written.
            filepath (str or Path): Path to write data.
        """
        mmcv.mkdir_or_exist(osp.dirname(filepath))
        with open(filepath, 'wb') as f:
            f.write(obj)

    def put_text(self,
                 obj: str,
                 filepath: Union[str, Path],
                 encoding: str = 'utf-8') -> None:
        """Write data to a given ``filepath`` with 'w' mode.

        Note:
            ``put_text`` will create a directory if the directory of
            ``filepath`` does not exist.

        Args:
            obj (str): Data to be written.
            filepath (str or Path): Path to write data.
            encoding (str): The encoding format used to open the ``filepath``.
                Default: 'utf-8'.
        """
        mmcv.mkdir_or_exist(osp.dirname(filepath))
        with open(filepath, 'w', encoding=encoding) as f:
            f.write(obj)

    def remove(self, filepath: Union[str, Path]) -> None:
        """Remove a file.

        Args:
            filepath (str or Path): Path to be removed.
        """
        os.remove(filepath)

    def exists(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path exists.

        Args:
            filepath (str or Path): Path to be checked whether exists.

        Returns:
            bool: Return ``True`` if ``filepath`` exists, ``False`` otherwise.
        """
        return osp.exists(filepath)

    def isdir(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a directory.

        Args:
            filepath (str or Path): Path to be checked whether it is a
                directory.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a directory,
                ``False`` otherwise.
        """
        return osp.isdir(filepath)

    def isfile(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a file.

        Args:
            filepath (str or Path): Path to be checked whether it is a file.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a file, ``False``
                otherwise.
        """
        return osp.isfile(filepath)

    def join_path(self, filepath: Union[str, Path],
                  *filepaths: Union[str, Path]) -> str:
        """Concatenate all file paths.

        Join one or more filepath components intelligently. The return value
        is the concatenation of filepath and any members of *filepaths.

        Args:
            filepath (str or Path): Path to be concatenated.

        Returns:
            str: The result of concatenation.
        """
        return osp.join(filepath, *filepaths)

    @contextmanager
    def get_local_path(
            self, filepath: Union[str, Path]) -> Iterable[Union[str, Path]]:
        """Only for unified API and do nothing."""
        yield filepath

    def list_dir_or_file(self,
                         dir_path: Union[str, Path],
                         list_dir: bool = True,
                         list_file: bool = True,
                         suffix: Optional[Union[str, Tuple[str]]] = None,
                         recursive: bool = False) -> Iterator[str]:
        """Scan a directory to find the interested directories or files in
        arbitrary order.

        Note:
            :meth:`list_dir_or_file` returns the path relative to ``dir_path``.

        Args:
            dir_path (str | Path): Path of the directory.
            list_dir (bool): List the directories. Default: True.
            list_file (bool): List the path of files. Default: True.
            suffix (str or tuple[str], optional):  File suffix
                that we are interested in. Default: None.
            recursive (bool): If set to True, recursively scan the
                directory. Default: False.

        Yields:
            Iterable[str]: A relative path to ``dir_path``.
        """
        if list_dir and suffix is not None:
            raise TypeError('`suffix` should be None when `list_dir` is True')

        if (suffix is not None) and not isinstance(suffix, (str, tuple)):
            raise TypeError('`suffix` must be a string or tuple of strings')

        root = dir_path

        def _list_dir_or_file(dir_path, list_dir, list_file, suffix,
                              recursive):
            for entry in os.scandir(dir_path):
                if not entry.name.startswith('.') and entry.is_file():
                    rel_path = osp.relpath(entry.path, root)
                    if (suffix is None
                            or rel_path.endswith(suffix)) and list_file:
                        yield rel_path
                elif osp.isdir(entry.path):
                    if list_dir:
                        rel_dir = osp.relpath(entry.path, root)
                        yield rel_dir
                    if recursive:
                        yield from _list_dir_or_file(entry.path, list_dir,
                                                     list_file, suffix,
                                                     recursive)

        return _list_dir_or_file(dir_path, list_dir, list_file, suffix,
                                 recursive)


class HTTPBackend(BaseStorageBackend):
    """HTTP and HTTPS storage bachend."""

    def get(self, filepath):
        value_buf = urlopen(filepath).read()
        return value_buf

    def get_text(self, filepath, encoding='utf-8'):
        value_buf = urlopen(filepath).read()
        return value_buf.decode(encoding)

    @contextmanager
    def get_local_path(self, filepath: str) -> Iterable[str]:
        """Download a file from ``filepath``.

        ``get_local_path`` is decorated by :meth:`contxtlib.contextmanager`. It
        can be called with ``with`` statement, and when exists from the
        ``with`` statement, the temporary path will be released.

        Args:
            filepath (str): Download a file from ``filepath``.

        Examples:
            >>> client = HTTPBackend()
            >>> # After existing from the ``with`` clause,
            >>> # the path will be removed
            >>> with client.get_local_path('http://path/of/your/file') as path:
            ...     # do something here
        """
        try:
            f = tempfile.NamedTemporaryFile(delete=False)
            f.write(self.get(filepath))
            f.close()
            yield f.name
        finally:
            os.remove(f.name)


class FileClient:
    """A general file client to access files in different backends.

    The client loads a file or text in a specified backend from its path
    and returns it as a binary or text file. There are two ways to choose a
    backend, the name of backend and the prefix of path. Although both of them
    can be used to choose a storage backend, ``backend`` has a higher priority
    that is if they are all set, the storage backend will be chosen by the
    backend argument. If they are all `None`, the disk backend will be chosen.
    Note that It can also register other backend accessor with a given name,
    prefixes, and backend class. In addition, We use the singleton pattern to
    avoid repeated object creation. If the arguments are the same, the same
    object will be returned.

    Args:
        backend (str, optional): The storage backend type. Options are "disk",
            "ceph", "memcached", "lmdb", "http" and "petrel". Default: None.
        prefix (str, optional): The prefix of the registered storage backend.
            Options are "s3", "http", "https". Default: None.

    Examples:
        >>> # only set backend
        >>> file_client = FileClient(backend='petrel')
        >>> # only set prefix
        >>> file_client = FileClient(prefix='s3')
        >>> # set both backend and prefix but use backend to choose client
        >>> file_client = FileClient(backend='petrel', prefix='s3')
        >>> # if the arguments are the same, the same object is returned
        >>> file_client1 = FileClient(backend='petrel')
        >>> file_client1 is file_client
        True

    Attributes:
        client (:obj:`BaseStorageBackend`): The backend object.
    """

    _backends = {
        'disk': HardDiskBackend,
        'ceph': CephBackend,
        'memcached': MemcachedBackend,
        'lmdb': LmdbBackend,
        'petrel': PetrelBackend,
        'http': HTTPBackend,
    }
    # This collection is used to record the overridden backends, and when a
    # backend appears in the collection, the singleton pattern is disabled for
    # that backend, because if the singleton pattern is used, then the object
    # returned will be the backend before overwriting
    _overridden_backends = set()
    _prefix_to_backends = {
        's3': PetrelBackend,
        'http': HTTPBackend,
        'https': HTTPBackend,
    }
    _overridden_prefixes = set()

    _instances = {}

    def __new__(cls, backend=None, prefix=None, **kwargs):
        if backend is None and prefix is None:
            backend = 'disk'
        if backend is not None and backend not in cls._backends:
            raise ValueError(
                f'Backend {backend} is not supported. Currently supported ones'
                f' are {list(cls._backends.keys())}')
        if prefix is not None and prefix not in cls._prefix_to_backends:
            raise ValueError(
                f'prefix {prefix} is not supported. Currently supported ones '
                f'are {list(cls._prefix_to_backends.keys())}')

        # concatenate the arguments to a unique key for determining whether
        # objects with the same arguments were created
        arg_key = f'{backend}:{prefix}'
        for key, value in kwargs.items():
            arg_key += f':{key}:{value}'

        # if a backend was overridden, it will create a new object
        if (arg_key in cls._instances
                and backend not in cls._overridden_backends
                and prefix not in cls._overridden_prefixes):
            _instance = cls._instances[arg_key]
        else:
            # create a new object and put it to _instance
            _instance = super().__new__(cls)
            if backend is not None:
                _instance.client = cls._backends[backend](**kwargs)
            else:
                _instance.client = cls._prefix_to_backends[prefix](**kwargs)

            cls._instances[arg_key] = _instance

        return _instance

    @property
    def name(self):
        return self.client.name

    @property
    def allow_symlink(self):
        return self.client.allow_symlink

    @staticmethod
    def parse_uri_prefix(uri: Union[str, Path]) -> Optional[str]:
        """Parse the prefix of a uri.

        Args:
            uri (str | Path): Uri to be parsed that contains the file prefix.

        Examples:
            >>> FileClient.parse_uri_prefix('s3://path/of/your/file')
            's3'

        Returns:
            str | None: Return the prefix of uri if the uri contains '://'
                else ``None``.
        """
        assert is_filepath(uri)
        uri = str(uri)
        if '://' not in uri:
            return None
        else:
            prefix, _ = uri.split('://')
            # In the case of PetrelBackend, the prefix may contains the cluster
            # name like clusterName:s3
            if ':' in prefix:
                _, prefix = prefix.split(':')
            return prefix

    @classmethod
    def infer_client(cls,
                     file_client_args: Optional[dict] = None,
                     uri: Optional[Union[str, Path]] = None) -> 'FileClient':
        """Infer a suitable file client based on the URI and arguments.

        Args:
            file_client_args (dict, optional): Arguments to instantiate a
                FileClient. Default: None.
            uri (str | Path, optional): Uri to be parsed that contains the file
                prefix. Default: None.

        Examples:
            >>> uri = 's3://path/of/your/file'
            >>> file_client = FileClient.infer_client(uri=uri)
            >>> file_client_args = {'backend': 'petrel'}
            >>> file_client = FileClient.infer_client(file_client_args)

        Returns:
            FileClient: Instantiated FileClient object.
        """
        assert file_client_args is not None or uri is not None
        if file_client_args is None:
            file_prefix = cls.parse_uri_prefix(uri)  # type: ignore
            return cls(prefix=file_prefix)
        else:
            return cls(**file_client_args)

    @classmethod
    def _register_backend(cls, name, backend, force=False, prefixes=None):
        if not isinstance(name, str):
            raise TypeError('the backend name should be a string, '
                            f'but got {type(name)}')
        if not inspect.isclass(backend):
            raise TypeError(
                f'backend should be a class but got {type(backend)}')
        if not issubclass(backend, BaseStorageBackend):
            raise TypeError(
                f'backend {backend} is not a subclass of BaseStorageBackend')
        if not force and name in cls._backends:
            raise KeyError(
                f'{name} is already registered as a storage backend, '
                'add "force=True" if you want to override it')

        if name in cls._backends and force:
            cls._overridden_backends.add(name)
        cls._backends[name] = backend

        if prefixes is not None:
            if isinstance(prefixes, str):
                prefixes = [prefixes]
            else:
                assert isinstance(prefixes, (list, tuple))
            for prefix in prefixes:
                if prefix not in cls._prefix_to_backends:
                    cls._prefix_to_backends[prefix] = backend
                elif (prefix in cls._prefix_to_backends) and force:
                    cls._overridden_prefixes.add(prefix)
                    cls._prefix_to_backends[prefix] = backend
                else:
                    raise KeyError(
                        f'{prefix} is already registered as a storage backend,'
                        ' add "force=True" if you want to override it')

    @classmethod
    def register_backend(cls, name, backend=None, force=False, prefixes=None):
        """Register a backend to FileClient.

        This method can be used as a normal class method or a decorator.

        .. code-block:: python

            class NewBackend(BaseStorageBackend):

                def get(self, filepath):
                    return filepath

                def get_text(self, filepath):
                    return filepath

            FileClient.register_backend('new', NewBackend)

        or

        .. code-block:: python

            @FileClient.register_backend('new')
            class NewBackend(BaseStorageBackend):

                def get(self, filepath):
                    return filepath

                def get_text(self, filepath):
                    return filepath

        Args:
            name (str): The name of the registered backend.
            backend (class, optional): The backend class to be registered,
                which must be a subclass of :class:`BaseStorageBackend`.
                When this method is used as a decorator, backend is None.
                Defaults to None.
            force (bool, optional): Whether to override the backend if the name
                has already been registered. Defaults to False.
            prefixes (str or list[str] or tuple[str], optional): The prefixes
                of the registered storage backend. Default: None.
                `New in version 1.3.15.`
        """
        if backend is not None:
            cls._register_backend(
                name, backend, force=force, prefixes=prefixes)
            return

        def _register(backend_cls):
            cls._register_backend(
                name, backend_cls, force=force, prefixes=prefixes)
            return backend_cls

        return _register

    def get(self, filepath: Union[str, Path]) -> Union[bytes, memoryview]:
        """Read data from a given ``filepath`` with 'rb' mode.

        Note:
            There are two types of return values for ``get``, one is ``bytes``
            and the other is ``memoryview``. The advantage of using memoryview
            is that you can avoid copying, and if you want to convert it to
            ``bytes``, you can use ``.tobytes()``.

        Args:
            filepath (str or Path): Path to read data.

        Returns:
            bytes | memoryview: Expected bytes object or a memory view of the
                bytes object.
        """
        return self.client.get(filepath)

    def get_text(self, filepath: Union[str, Path], encoding='utf-8') -> str:
        """Read data from a given ``filepath`` with 'r' mode.

        Args:
            filepath (str or Path): Path to read data.
            encoding (str): The encoding format used to open the ``filepath``.
                Default: 'utf-8'.

        Returns:
            str: Expected text reading from ``filepath``.
        """
        return self.client.get_text(filepath, encoding)

    def put(self, obj: bytes, filepath: Union[str, Path]) -> None:
        """Write data to a given ``filepath`` with 'wb' mode.

        Note:
            ``put`` should create a directory if the directory of ``filepath``
            does not exist.

        Args:
            obj (bytes): Data to be written.
            filepath (str or Path): Path to write data.
        """
        self.client.put(obj, filepath)

    def put_text(self, obj: str, filepath: Union[str, Path]) -> None:
        """Write data to a given ``filepath`` with 'w' mode.

        Note:
            ``put_text`` should create a directory if the directory of
            ``filepath`` does not exist.

        Args:
            obj (str): Data to be written.
            filepath (str or Path): Path to write data.
            encoding (str, optional): The encoding format used to open the
                `filepath`. Default: 'utf-8'.
        """
        self.client.put_text(obj, filepath)

    def remove(self, filepath: Union[str, Path]) -> None:
        """Remove a file.

        Args:
            filepath (str, Path): Path to be removed.
        """
        self.client.remove(filepath)

    def exists(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path exists.

        Args:
            filepath (str or Path): Path to be checked whether exists.

        Returns:
            bool: Return ``True`` if ``filepath`` exists, ``False`` otherwise.
        """
        return self.client.exists(filepath)

    def isdir(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a directory.

        Args:
            filepath (str or Path): Path to be checked whether it is a
                directory.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a directory,
                ``False`` otherwise.
        """
        return self.client.isdir(filepath)

    def isfile(self, filepath: Union[str, Path]) -> bool:
        """Check whether a file path is a file.

        Args:
            filepath (str or Path): Path to be checked whether it is a file.

        Returns:
            bool: Return ``True`` if ``filepath`` points to a file, ``False``
                otherwise.
        """
        return self.client.isfile(filepath)

    def join_path(self, filepath: Union[str, Path],
                  *filepaths: Union[str, Path]) -> str:
        """Concatenate all file paths.

        Join one or more filepath components intelligently. The return value
        is the concatenation of filepath and any members of *filepaths.

        Args:
            filepath (str or Path): Path to be concatenated.

        Returns:
            str: The result of concatenation.
        """
        return self.client.join_path(filepath, *filepaths)

    @contextmanager
    def get_local_path(self, filepath: Union[str, Path]) -> Iterable[str]:
        """Download data from ``filepath`` and write the data to local path.

        ``get_local_path`` is decorated by :meth:`contxtlib.contextmanager`. It
        can be called with ``with`` statement, and when exists from the
        ``with`` statement, the temporary path will be released.

        Note:
            If the ``filepath`` is a local path, just return itself.

        .. warning::
            ``get_local_path`` is an experimental interface that may change in
            the future.

        Args:
            filepath (str or Path): Path to be read data.

        Examples:
            >>> file_client = FileClient(prefix='s3')
            >>> with file_client.get_local_path('s3://bucket/abc.jpg') as path:
            ...     # do something here

        Yields:
            Iterable[str]: Only yield one path.
        """
        with self.client.get_local_path(str(filepath)) as local_path:
            yield local_path

    def list_dir_or_file(self,
                         dir_path: Union[str, Path],
                         list_dir: bool = True,
                         list_file: bool = True,
                         suffix: Optional[Union[str, Tuple[str]]] = None,
                         recursive: bool = False) -> Iterator[str]:
        """Scan a directory to find the interested directories or files in
        arbitrary order.

        Note:
            :meth:`list_dir_or_file` returns the path relative to ``dir_path``.

        Args:
            dir_path (str | Path): Path of the directory.
            list_dir (bool): List the directories. Default: True.
            list_file (bool): List the path of files. Default: True.
            suffix (str or tuple[str], optional):  File suffix
                that we are interested in. Default: None.
            recursive (bool): If set to True, recursively scan the
                directory. Default: False.

        Yields:
            Iterable[str]: A relative path to ``dir_path``.
        """
        yield from self.client.list_dir_or_file(dir_path, list_dir, list_file,
                                                suffix, recursive)